The invention relates to automatic apparatus for separating alternately facing fabric workpieces from a single stack into two separate stacks.
It is often desirable in the garment fabrication industry to separate layers of stacked fabric workpieces from each other and to transport them to other work stations. Such prior art separating devices are described in U.S. Pat. Nos. 3,253,824 and 3,042,505. As pointed out in those patents, separating stacked fabric layers is extremely difficult since the layers of fabric, during cutting, tend to have their end threads interwoven and are thereby bonded together. It requires considerable ingenuity to separate each layer of fabric from this bonding interengagement of the end threads without simultaneously disrupting the placement of the layers in the stack.
It is desirable not to disturb the placement of the layers in the stack in order that the workpieces may be accurately aligned with respect to the separating apparatus and so that after separation they can be transported to another work station with a predetermined orientation. If the fabric layers are misaligned, they will not be properly transported in an aligned relationship to the next work station, but, instead, will be mis-positioned upon reaching the subsequent work station.
The mechanisms for separating such layers of stacked fabric workpieces are known in the trade as differentiators. The differentiators described in the above two referenced patents rely on a clamping member working in conjunction with a rotating friction member to peel back a layer of fabric while holding the remaining stack stationary. This type of differentiator has many disadvantages well known to the trade, among them, the problem that it does not easily adapt to different types of fabric, nor is it entirely effective in separating the layers without disturbing the underlying layers or picking up more than one layer of fabric at the same time.
More suitable types of differentiators are described in U.S. Pat. Nos. 793,009 (Miller) and 3,981,495 (Bijttebier) which disclose a pair of horizontal, rotatable cylinders having needles which project in opposite directions and which are lowered to rest on the top fabric layer of a stack of fabric workpieces. The cylinders are counter-rotated to drive the needles into the top layer and then are lifted to pull away the top layer from the stack. This type of differentiating head is more effective than other types of differentiating heads for some applications. However, it also suffers from a disadvantage in that unless the needles penetrate the fabric evenly when the cylinders are counter-rotated there may be a tendency to shift the top layer horizontally, thus causing it to be misaligned.
In one garment industry operation, left and right pocket facings are cut simultaneously on a spreading table from a fabric stack having alternately face-up and face-down layers. The result is a plurality of smaller stacks of alternating left and right facing plies. It then becomes necessary to separate these left and right facing plies into two separate stacks of all left and all right facing plies. In order to do this automatically, it is not only necessary to effectively separate the alternate left and right facing plies from the stack without misalignment, as described above, but it is also necessary to detect whether the stack somehow contains two facing plies oriented in the same direction, that is, face-up or face-down. It is further necessary to detect whether one of the differentiated plies has been dropped by the differentiating head since this would cause one of the stacks to be short in the number of facing plies.